Traveling wave tubes which have intersecting electric and magnetic fields and are pulse modulated



March l5, 1955 A. LERBS 2,704,350

TRAVELINC wAvE TUBES WHICH-HAVE INTERSECTINC ELECTRIC AND MAGNETIC FIELDS AND ARE PULSE MCDULATED Filed Maren 1e, 1954 FIG.5

United States Patent O TRAVELING WAVE TUBES WHICH HAVE INTER- SECTING ELECTRIC AND MAGNETIC FIELDS AND ARE PULSE MODULATED Alfred Lerbs, Paris, France, assignor to Compagnie Generale de Telegraphie Sans Fil, a corporation of France Application March 16, 1954, Serial No. 416,650

Claims priority, application France March 18, 1953 3 Claims. (Cl. 332-13) Tubes are known that operate as ultra-high frequency amplifiers, oscillators or multipliers in which the electron beam is propagated in a direction perpendicular to an electric eld and a magnetic field which are themselves perpendicular to one another. The electric field is established between two electrodes which are substantially parallel to the beam, the positive electrode or anode being formed by a delay line. The ratio between the two fields is so adjusted that the beam is propagated with a velocity equal to the phase velocity of a component of the field of the ultra-high frequency wave that is propagated in the delay line.

When pulse modulating the output of such tubes, the simplest solution seems to apply modulating pulses to the emitting cathode so that the electric field exists between the electrodes only during the pulses. Now, the tubes in question function correctly, with a constant magnetic field, for a single value only of the electric field. It is therefore necessary that the pulses have very steep anks. Now, it is diicult to obtain satisfactory pulses with conventional modulators.

The present invention has for object to provide a tube of the above-mentioned type which is particularly suitable for pulse modulation.

According to the invention the negative electrode of the tube is divided into two sections, the first section being situated in front of the anode and maintained at a fixed D. C. potential and the second section supporting the cathode and being connected to the modulator. The second section is brought, for the duration of the pulses, to a potential in the neighborhood of the irst section. In the intervals of time between the pulses it remains at the potential of the anode. In this way the cathode only emits during duration of the pulses. It is blocked for the rest of the time.

Preferably, the potential of the second section is, for the duration of the pulses, more negative than that of the first section.

The invention will be better understood from the ensuing description with reference to the accompanying drawings, wherein,

Fig. 1 is a longitudinal sectional view of a first em bodiment of the invention;

Fig. 2 is a diagrammatic view of the tube shown in Fig. l, seen from one end;

Fig. 3 is a longitudinal sectional view of a second embodiment of the tube according to the invention.

Fig. 1 shows diagrammatically a traveling wave tube of the aforementioned type, which is rectilinear and opcrates as an amplifier. It comprises, within an envelope 1, a delay line 2 and a negative electrode 4 which is parallel to the latter. The delay line 2 and the Aenvelope 1 are earthed. Ultra-high frequency energy is fed to the line 2 through the input 6 and the energy amplified by the tube is collected at the output 15. The electrode 4 is brought to a negative potential by a source of D. C. voltage 11 connected to the terminals 14, one of which is connected to the electrode 4 and the other to earth. A resistance 16 which is shunted by a capacitor 13, is connected across the terminals 14. Another electrode section 7, which is negative and in alignment with the electrode 4, supports an emitting cathode 3 which is at the same potential as the electrode 7. This cathode is heated by a filament 5 one end of which is connected directly to the electrode 7. The space between, on the one hand, the electrode 2 and, on the other, the electrodes tage.

4 and 7, is subjected to a magnetic ield B which is perpendicular to the plane of the gure and is created, for example, by polar elements 22, shown in Fig. 2.

The modulating voltage is fed through the terminals 19 to the primary winding 18 of a transformer having two secondary windings 17 and 8 which are inserted in series in the heating circuit. The heating voltage is taken from the secondary of a transformer 9, the primary of this transformer being fed through the terminals 20 from the mains. The winding 17 is earthed through a resistor 10 and the winding 8 is separated from earth by the capacitor 12. The latter is high enough to allow the pulses through. In this way, the electrode 7 is brought to the ground potential i. e. the anode potential. During the pulses the potential of the electrode 7 becomes negative.

In the described arrangement, the secondary winding of the heating transformer 9 does not require high voltage insulation, which constitutes a considerable advan- Further, the only capacitance which is in parallel with the cathode-beam-collector circuit is the capacitance built up by the electrode 7 and the portion of the electrode opposite this electrode. This capacitance is relatively small. It provides therefore an important impedance to the pulses. The latter are therefore not distorted and retain steep edges. The manner in which the two secondary windings are disposed in the heating conductors decreases the actual capacity between the primary and secondary windings of this transformer.

It will be noted that the electric field is constant in the space between the electrodes 2 and 4 for the whole cycle of modulation.

In Fig. 3 like reference numerals designate like elements shown in Fig. 1.

The cathode 3 has its lament connected to the two terminals 20 of the secondary winding of the transformer 9. The primary of this transformer is fed by the mains supply. One of the terminals of the secondary. of the transformer 9 is connected to the terminal of the secondary 17 of a pulse transformer. The second terminal of this secondary is earthed. The two terminals of the primary 18 of this transformer are connected to the pulse modulator.

The negative electrode 4 is brought to a high negative D. C. voltage by the source 11 to which it is connected through one of the terminals 14.

This second arrangement has the advantage of being very simple, but the secondary winding of the transformer 9 must be insulated from earth.

In my case it is advantageous to provide a specially designed electron optical system; for example it is advisable to give to the electrode 7 the profile shown in Fig. l in order to avoid deformations of the electric eld on account of the potential difference between the electrodes 4 and 7.

What I claim is:

1. A traveling wave tube of the type including an anode in the form of a delay line, means for propagating an ultra-high frequency wave along said delay line, a negative electrode parallel thereto, whereby an electric field is provided between said two electrodes, means for providing within said tube a magnetic field normal to said electric eld, a cathode for propagating an electron beam normally to both said fields, and a collector electrode for collecting said beam, said tube comprising: an auxiliary electrode located substantially in prolongation of said negative electrode, said auxiliary electrode supporting said cathode; energized connections for positively biasing said auxiliary electrode, whereby said cathode is normally blocked; and connections for applying modulating pulses provided by a modulating source between said auxiliary electrode and said delay line, with negative potential of said pulses applied to said auxiliary electrode, for causing said cathode to emit during each of said pulses.

2. A traveling wave tube of the type including an anode in the form of a delay line, means for propagating an ultra-high frequency wave along said delay line, a negative electrode parallel thereto, whereby an electric ield is provided between said two electrodes, means for providing within said tube a magnetic eld normal to said electric eld, a cathode for propagating an electron beam normally to both said fields, and a collector electrode for collecting said beam, said tube comprising: an auxiliary electrode located substantially in prolongation of said negative electrode, said auxiliary electrode supporting said cathode, connections from said auxiliary electrode to said delay line, whereby said cathode is normally blocked; and connections for applying modulating pulses provided by a modulating source between said auxiliary electrode and said delay line with negative potential of said pulses applied to said auxiliary electrode, for causing said cathode to emit during each of said pulses.

3. A traveling wave tube of the type including an anode in the form of a delay line, means for propagating an ultrahigh frequency wave along said delay line, a negative electrode parallel thereto, whereby an electric eld is provided between said two electrodes, means for providing within said tube a magnetic eld normal to said electric field, a cathode for propagating an electron beam normally to both said lields, and a collector electrode for collecting said beam, said tube comprising: an auxiliary electrode located substantially in prolongation of said negative electrode, said auxiliary electrode supporting said cathode; connections from said auxiliary electrode to said delay line, whereby said cathode is normally blocked; a heating circuit of said cathode electrically connected to said auxiliary electrode; a modulating source, coupling means between said modulating source and said heating circuit, for applying modulating pulses between said auxiliary electrode and said delay line with negative potentials of said pulses applied to said auxiliary electrode, for causing said cathode to emit during each of said pulses.

No references cited. 

